Non-ferrous metal ingots and billets are formed by casting in a vertically oriented mold, which is generally situated above a large casting pit beneath the floor level of the casting facility. The lower component of the vertical casting mold is a starting block mounted on starting block pedestals. When the casting process begins, the starting blocks are in their upward-most position and in the molds. As molten non-ferrous metal is poured into the mold and cooled, the starting block is slowly lowered at a pre-determined rate by a hydraulic cylinder. As the starting block is lowered, solidified non-ferrous metal or aluminum emerges from the bottom of the mold and ingots or billets are formed.
While the invention applies to casting and rotational control during the casting of non-ferrous metals, including aluminum, brass, lead, zinc, magnesium, copper etc., the examples given and preferred embodiment disclosed are for aluminum, and therefore the term aluminum will be used throughout for consistency even though the invention applies more generally to non-ferrous metals.
As shown in FIG. 1, the vertical casting of aluminum generally occurs beneath the elevation level of the factory floor in a casting pit. Directly beneath the casting pit floor 1a is a caisson 3, in which the hydraulic cylinder barrel 2 for the hydraulic cylinder is placed.
As shown in FIG. 1, the components of the lower portion of a typical vertical aluminum casting apparatus, shown within a casting pit 1 and a caisson 3, are a hydraulic cylinder barrel 2, a ram 6, a mounting base housing 5, a platen 7 and a starting block base 8, all shown at elevations below the casting facility floor 4.
Although the hydraulic cylinder barrel 2 is referred to as such in the industry and herein, for purposes of this invention, it is a vertically oriented elongated enclosure with a hollow interior and can be any shape or configuration. Further, while the term ram 6 is used herein to refer to the component so identified, it is also sometimes referred to as a piston or a piston rod, but for consistency herein will be referred to as a ram or hydraulic ram. The ram is a sliding component which moves back and forth against fluid pressure, as described more fully herein.
The mounting base housing 5 is mounted to the floor 1a of the casting pit 1, below which is the caisson 3. The caisson 3 is defined by its side walls 3b and its floor 3a.
A torque limiter 9 interconnects the platen 7 and the ram 6 to protect the ram 6 and related parts in the event of a severe rotational force, in which case the torque limiter 9 will cause the connection between the platen 7 and the ram 6 to release and allow the platen 7 to rotate without damaging the ram 6 or parts connected to the ram 6. A typical mold table assembly 10 is also shown in FIG. 1, which can be tilted as shown by hydraulic cylinder 11 pushing mold table tilt arm 10a such that it pivots about point 12 and thereby raises and rotates the main casting frame assembly, as shown in FIG. 1. There are also mold table carriages which allow the mold table assemblies to be moved from the position above the casting pit.
FIG. 1 further shows the platen 7 and starting block base 8 partially descended into the casting pit 1 with billet 13 being partially formed. Billet 13 is on starting block 14, which is mounted on pedestal 15. While the term starting block is used for item 14, it should be noted that the terms bottom block and starting head are also used in the industry to refer to item 14, bottom block typically used when an ingot is being cast and starting head when a billet is being cast.
While the starting block base 8 in FIG. 1 only shows one starting block 14 and pedestal 15, there are typically several of each mounted on each starting block base, which simultaneously cast billets or ingots as the starting block is lowered during the casting process.
The upper portion of the aluminum casting apparatus includes a vertical aluminum mold table assembly 10 and tilts to the upward position shown in FIG. 1.
When hydraulic fluid is introduced into the hydraulic cylinder at sufficient pressure, the ram 6, and consequently the starting block base 8, are raised to the desired elevation start level for the casting process, which is when the starting blocks are within the mold table assembly 10.
The lowering of the starting block base 8 is accomplished by metering the hydraulic fluid from the cylinder at a pre-determined rate, thereby lowering the ram 6 and consequently the starting blocks at a pre-determined and controlled rate. The mold is controllably cooled during the process to assist in the solidification of the emerging ingots or billets, typically using water cooling means.
It is critical to the resulting quality of the finished aluminum ingots or billets to maintain true vertical movement without unacceptable rotation of the starting block during the casting process. Very slight rotation of the starting block while it is being lowered during the casting process can result in significant imperfections in the ingots and billets and rejection of the several ingots and billets being simultaneously cast in that particular casting batch.
Prior art generally provides rotational guidance systems of two types, internal and external.
In the external guidance systems, the platen is guided by vertical guide rails which are mounted to the side walls of the casting pit. The platen in these external systems has mating shoes which slide along the guide rails while the starting block base is lowered, thereby restricting the rotation of the platen during casting.
While these external rotational guidance systems can maintain low tolerances, the vertical guide rails and mating shoes are exposed to the harsh environment of an aluminum casting facility. This results in the buildup of dirt, debris and molten metal from aluminum spills on both the guide rails and the mating shoes. When buildup occurs, it not only affects the rotational stability, but can also result in the stoppage of the vertical movement of the starting block base, which freezes the billet or ingot in the mold in the middle of a cast and is very time consuming and difficult to remedy.
Internal rotational guidance systems are intended to prevent the unacceptable rotation of the starting block base while also avoiding the problems associated with external systems due to the environmental and operating conditions.
One form of an internal system is shown in FIG. 2, which illustrates a hydraulic cylinder barrel 2, a ram 6, barrel flange 19 and mounting base housing 5. The internal guide rail 20 is welded along the entire vertical length of the interior wall of the hollow hydraulic cylinder barrel 2. A guide 31 is mounted on and extends outwardly from the ram and mates with a guide rail 20 on the interior wall of the hydraulic cylinder barrel 2. As the ram 6 is raised, the guide 31 slides along the guide rail 20 to maintain the ram 6 in fixed rotational alignment.
FIG. 3 shows a cross-section from FIG. 2, illustrating the guide 31 with guide rail interfaces 34 defining an aperture which corresponds to the guide rail 20 shown in FIG. 2.
In order to meet the requisite accuracies for aluminum castings, the welding of the guide rail 20 along the entire length of the interior of the hydraulic cylinder barrel 2 requires substantial time and expense. Furthermore, utilizing such a guidance system with a key external to the ram 6 and internal to the hydraulic cylinder barrel 2, requires that the diameter of the hydraulic cylinder barrel 2 and consequently of the caisson, be unnecessarily large.
The size of the caissons 3 for existing external rotational guidance systems is smaller than for the internal rotational guidance system because the additional size of the mating guide does not have to be accommodated. The numerous aluminum casting pits yet to be converted from an external rotational guidance system to an internal rotational guidance system will require substantial excavation of the factory floor to make the existing pits and caissons larger to convert or upgrade to the larger diameter internal guidance systems. Making modifications to casting pits and caissons within existing factories is undesirable due to the expense and disruption.
FIG. 4 illustrates a cross-section of another attempt to maintain internal rotational control during the aluminum casting process. Figure 4 shows a hydraulic cylinder barrel 40, a ram 41 and a guide 42. The guide 42 is attached to the bottom of the ram 41 in similar fashion to the guide 31 illustrated in FIG. 2.
As shown in FIG. 4, a square or rectangular aperture 44 is defined within the longitudinal center of the ram 6. Located within the aperture 44 is a corresponding center guide key 43. When the ram moves vertically, the corresponding surfaces of the aperture 44 and the center guide key 43 are intended to prevent the rotation of the starting block base during the casting process.
While the internal rotational control system shown in FIG. 4 has the advantage of a smaller hydraulic cylinder barrel and is adaptable to existing smaller diameter caissons, it is unable to achieve the tolerances demanded in the industry because the contact surfaces are too near the center of rotation, thus having very little rotational control.
The need for an internal rotational guidance system which can be utilized in existing casting pits and caissons and which can meet the tolerance requirements of the aluminum industry has been recognized, but has not been adequately fulfilled by prior known machinery or methods.
A further need has been recognized for such a rotational stabilization system that can easily be installed within existing casting pits and caissons, without the need for substantial modification to accommodate the larger diameter hydraulic cylinder barrel required by internal systems which utilize a guide external to the ram and internal to the hydraulic cylinder barrel.
A still further need has been recognized for an environmentally protected rotational stabilization system which does not require the substantial time and expense in welding a guide key along the entire vertical length of the interior of the hydraulic cylinder barrel, such as is required by the internal systems which utilize a mating guide external to the ram and internal to the hydraulic cylinder barrel.
The forenamed recognized needs have not heretofore been sufficiently fulfilled by existing rotational control and guide systems.
The present invention is an internal rotational guidance system for vertical aluminum casting machines which meets or exceeds the desired tolerance levels of the aluminum casting industry and which accomplishes this within a much smaller cross-sectional area, thus having the further advantage of being easily installed in existing casting pits and caissons which cannot accommodate the larger diameter barrel tubes without substantial modification thereto.